The closest known process and apparatus to that of this invention, is described in my U.S. Pat. No. 5,019,331, issued May 28, 1991 for "PROCESS FOR THE PRODUCTION OF MATERIALS AND MATERIALS PRODUCED BY THE PROCESS"; its parent application, U.S. Ser. No. 07/314,651, filed Feb. 23, 1989, now abandoned; its divisional application Ser. No. 07/571,075 filed Aug. 21, 1990, now U.S. Pat. No. 5,147,722, issued Sep. 15, 1992; and the references cited therein.
The above-mentioned U.S. Pat. No. 5,019,311 discloses the production of composite materials which are characterized by primary particles interconnected by a continuous web matrix or by forced point-bonds, resulting from the presence of a binder material. The process requires high pressures and sufficient shear that are only applied shortly after heating the powdered feed material. One of the production techniques disclosed in the referenced application is extrusion through a die. (Application Sec. VI C., D.).
It has since been discovered that a number of practical problems arise in attempting to practice die extrusion to produce such composite solid articles, for example, activated carbon filters. While actual production of such articles can be achieved, it is only with difficulty. One reason is that, in order to achieve the high pressures and shear required after the heating step, it has been necessary to employ what are called "compression" dies. These are dies with decreasing cross-sections and dies in which a cross-section thereof is smaller than the cross-section of the extruder screw in order to produce substantial back pressure. The replication of these dies is extremely difficult due to a number of critical design factors such as the surface finish of the die and the depth and location of steps within the die. As a result of the complex design of such dies, they are extremely difficult to replicate and are very expensive. Furthermore, the difficulty of achieving correct back pressure based upon the internal configuration of the die passage is very difficult, can not be sufficiently controlled by the extruder operator, and results in a substantial amount of scrap.
It is therefore an object of this invention to provide a process and apparatus for extruding composite solid articles which eliminate or substantially avoid these drawbacks and problems. A further object of this invention is to produce novel composite solid articles, such as certain activated carbon filters, employing the process and apparatus.